1. Field of the Invention
This invention relates to an internal combustion engine provided with an auxiliary combustion chamber having no intake valve and designed to effect scavenging with a stream of sucked gas.
2. Description of the Prior Art
Various methods have been proposed to eliminate toxic substances contained in the exhaust gases from internal combustion engines. One of those methods consists of burning a lean fuel-air mixture. This is a very effective method, taking advantage of the fact that burning a fuel-air mixture with a large proportion of air reduces toxic substances, especially NOx, in the exhaust gases.
Usually, lean fuel-air mixtures are not readily ignited and slowly propagate the flame, which decreases the thermal efficiency of the cycle and gives rise to the problem of after-burning. This phenomenon occurs when the caloric force of an ignition source, which sets fire to the lean fuel-air mixture, is weak. Accordingly, this problem can be solved by increasing the ignition caloric force. To realize this solution, it was proposed to provide an auxiliary combustion chamber in addition to a main combustion chamber so that a lean fuel-air mixture in the latter chamber will be ignited by the flame from the former chamber. In a typical example of this type, a relatively rich fuel-air mixture is supplied to the auxiliary combustion chamber through an intake valve fitted thereto. This relatively rich fuel-air mixture in the auxiliary combustion chamber is ignited and burnt by an ignition spark plug. The flame thus produced flows into the main combustion chamber to burn a lean fuel-air mixture therein. This method is very effective because ignition in the auxiliary combustion chamber can be readily accomplished. However, the structure of the auxiliary combustion chamber became complex, because of the necessity of providing the intake valve therefor.
There is another method that provides an auxiliary combustion chamber having no intake valve adjacent to the main combustion chamber. According to this method, a lean fuel-air mixture in the main combustion chamber is forced into the aforesaid auxiliary combustion chamber on the compression stroke and ignited by the ignition spark plug. The flame produced is sent into the main combustion chamber to burn the lean fuel-air mixture therein. This method has a shortcoming that the exhaust gases resulting from the combustion on the preceding stroke remain in the auxiliary combustion chamber, which makes it difficult to ignite the mixture on the next stroke.
To do away with this shortcoming, the inventors have previously proposed an internal combustion engine that comprises a main and auxiliary combustion chamber communicated by a plurality of passages, wherein part of the passages is directed toward a stream of sucked air in order to scavenge the auxiliary combustion chamber.